Force transfer means for operation of a circuit breaker including rollers on an auxiliary operator and the circuit breaker handle

ABSTRACT

An auxiliary mechanism for operating a circuit breaker handle is provided with a lever carrying spaced straight rollers that engage a handle mounted straight roller positioned therebetween, with the axis of the handle roller being at right angles to the axes of the lever mounted rollers. The lever and handle pivot are in perpendicular planes, and the axis for the handle roller is at right angles to the plane of movement for the handle.

United States Patent 91 Strobel FORCE TRANSFER MEANS FOR OPERATION OF ACIRCUIT BREAKER INCLUDING ROLLERS ON AN AUXILIARY OPERATOR AND THECIRCUIT BREAKER HANDLE [75] Inventor: Albert Strobel, Cherry Hill, NJ.

[73] Assignee: I-T-E Imperial Corporation,

Philadelphia, Pa.

[22] Filed: July 27, 1972 [21] Appl. No.: 275,507

[52] US. Cl. ..200/330 [51] Int. Cl. "01h 3/02 [58] Field of Search200/172 A, 172 R, 153 H [56] References Cited UNITED STATES PATENTS2,240.922 5/1941 Bissell 200/172 A UX 2,277,645 3/1942 Johnson 200/172 A[451 Mar. 26, 1974 1,989,393 l/l935 Anderson 200/172 A FOREIGN PATENTSOR APPLICATIONS 1,161,310 8/1969 Great Britain 200/172 A PrimaryExaminerl-lerman Hohauser Assistant Examiner-Robert A. VanderhyeAttorney, Agent, or Firm0str0lenk, Faber, Gerb &

Soffen [5 7] ABSTRACT 5 Claims, 6 Drawing Figures wimmmzs m4 SHEET .1[IF NwN ATENTED R26 I974 SHEET 3 [IF 5 PATENTEUIARZG 1914 SHEET [1F 5FORCE TRANSFER MEANS FOR OPERATION OF A CIRCUIT BREAKER INCLUDINGROLLERS ON AN AUXILIARY OPERATOR AND THE CIRCUIT BREAKER HANDLE Thisinvention relates to molded case circuit breakers in general and moreparticularly relates to a low friction auxiliary mechanism for operatingthe circuit breaker handle.

Auxiliary mechanisms for operating molded case circuit breakers areoften provided with a fork-shaped lever that embraces an extension ofthe circuit breaker operating handle. The latter is pivoted in a planeperpendicular to the plane of movement for the lever so thatconsiderable friction exists between the engaging parts, with the leverusually being constructed of metal and the circuit breaker handle beingconstructed of plastic.

This friction results from the continuously changing point of contactbetween the lever and the handle due to the changing point ofintersection, causing the lever to slide up and down on the handle whilebeing subject to considerable pressure. As the metal lever digs into therelatively soft plastic handle, a rough recess forms in the handleadding further to the friction resisting operation of the auxiliarymechanism.

The prior art has sought to overcome this problem by adding abarrel-shaped roller to each side of the forkshaped lever. This was onlypartially successful in that the barrel shape of each roller was only arough approach to the changing line of contact between lever and handleso that the rollers on the fork dug into the handle. It appears that aclose-tolerance design for the exterior of the roller cannot be achievedeconomically because of the large number of components involved in acircuit breaker and an auxiliary handle mechanism therefor.

In accordance with the instant invention, the forkshaped lever of theauxiliary mechanism is provided with spaced straight, rather thanbarrel-shaped, metal rollers that engage another straight metal rolleron the circuit breaker handle. The fork and handle move in planes atright angles to one another, the rollers on the fork rotate on axesperpendicular to the plane of movement of the fork, and the roller onthe handle rotates about an axis perpendicular to the plane of movementfor the handle.

Since the ratio of roller outside diameter to roller shaft diameter islarge and each roller is free to rotate, only rolling friction willexist at the point of contact between rollers. The only sliding frictionwill occur at the relatively small diameter roller shafts where frictionforce moments will be very low because of small radii. Digging into thehandle will not occur so that force requirements at the operating handlewill remain constant for a reasonable number of operations.

Accordingly, a primary object of the instant invention is to provide anovel engaging means at the point of intersection between a circuitbreaker handle and an auxiliary mechanism for operating the handle.

Another object is to provide engaging means of this type that iseconomical to construct.

Still another object is to provide engaging means of this type soconstructed that friction forces are substantially eliminated.

A further object is to provide engaging means of this type soconstructed that handle force requirements will remain constant aftermany operations of the handle.

These objects as well as other objects of this invention will becomereadily apparent after reading the following description of theaccompanying drawings in which:

FIG. 1 is a plan view of a circuit breaker constructed in accordancewith teachings of the instant invention.

FIG. 2 is a longitudinal cross-section taken through line 22 of FIG. 1,looking in the direction of arrows 22, and including an auxiliary handleoperating mechanism not shown in FIG. 1.

FIG. 3 is an exploded perspective of one overcenter toggle mechanism andselected elements connected thereto.

FIG. 4 is an exploded perspective of the movable contact structure forone phase.

FIG. 5 is an enlarged longitudinal cross-section of the auxiliary handleoperating mechanism taken at right angles to the section of FIG. 2.

FIG. 6 is a cross-section taken through line 6-6 of FIG. 5 looking inthe direction of arrows 66.

Now referring to the figures. Three phase molded case circuit breaker 25of F168. 1 and 2 includes an individual overcenter spring-powered toggleoperating mechanism. Prior art examples of circuit breakers having morethan a single operating mechanism for all phases are disclosed in U.S.Pat. Nos. 2,067,935 and 3,125,653.

Circuit breaker 25 includes a molded housing constructed of base 26 andremovable cover 27 joined along line 28, and provided with longitudinalinternal partitions 31, 32 which divide housing 26, 27 into threelongitudinally extending compartments, one for each phase of circuitbreaker 25. Cover 27 is provided with aperture 29 through which stubbybifurcated extension 33 of operating handle means 30 extends. Eachsection of handle extension 33 receives an individual pin 34 extendingupwardly from the web portion of inverted generally U-shaped operatingyoke member 35 of the center phase. Operating members 35 of the outerphases are each secured to handle means 30 by a pair of screws 152.

Member 35 is pivoted to the spaced arms of generally U-shaped operatingmechanism frame 36 at outwardly extending lugs 37. Bolts 48, received bythreaded apertures of inturned edges 36a at the bottom of frame 36,fixedly secure the latter to base 26. Transverse tie member 49 isriveted to the arms of frame 36 to maintain spacing therebetween and tostabilize the frame structure.

Four-tensioned coil springs 38, each connected at one end thereof to theweb of operating member 35, combine to constitute the main operatingspring means for the overcenter toggle-type contact operating mechanism.The other ends of springs 38 are connected to spaced plates 39, 39 thatare pivotally mounted to toggle knee pin 41 connecting upper 42 andlower 43 toggle links. The upper ends of upper toggle links 42 arepivotally connected to the spaced arms of latchable cradle 40 at pins44, and the lower ends of lower toggle links 43 are pivotally connectedto contact carrier 45 by rod 46 that extends between the spaced arms ofcontact carrier 45. The spaced arms of cradle 40 are positioned adjacentthe inner surfaces of the spaced arms of frame 36 and are pivotallyconnected thereto by pins 47 that are secured to frame 36.

Under normal operating conditions plate 51, secured to web 40a of cradle40, is in engagement with forward latching surface 52 of auxiliary latch53. The latter is loosely mounted to pivot rod 55 extending between thespaced arm of mechanism frame 36 and slightly outboard thereof. Thecoiled end sections of torsion spring member 56 are wound about pivotrod 55, with the ends of these sections bearing against rod 57 andauxiliary latch 53 to bias the latter counterclockwise against stop rod58. The ends of rods 57 and 58 are supported by the arms of frame 36.Leaf spring 73 secured to auxiliary latch 53 bears against pivot rod 55biasing latch 53, so that rod 55 will normally lie at the centralportion of V-shaped notch 74 of primary latch 53.

The ends of rod 55 projecting outboard of mechanism frame 36 are engagedby the hooked portions at the forward extensions 59 of the arms forU-shaped trip unit frame 60, whose web portion is seated on a forwardsurface of load strap 61, being secured thereto by bolts 62 that extendthrough clearance apertures in strap 61 and are received by threadedinserts molded in base 26.

Rear latch tip 54 engages latch tip 63 at the U-shaped forward arm ofprimary latch 65, whose rear latch tip 64 is engaged by latch plate 67mounted on one leg of L-shaped carrier 66. Primary latch 65 is pivotallymounted to trip unit frame 60 at stub shaft 69, and the carrier ispivoted on rod 68 to frame 60. Tension spring 75 biases primary latch 65in a clockwise direction about pivot 69. The other leg of carrier 66 isprovided with transversely extending pin 71 that projects intotriangular window 72 of primary latch 65 at a portion thereof near rearlatch tip 64, for a reason to be hereinafter explained. Tension spring76, connected between frame 60 and carrier extension 660, biases carrier66 in a counterclockwise direction about its pivot 68 toward latchingposition.

When automatic tripping occurs, carrier 66 in the faulted phase is movedclockwise either by the deflection of bimetal. 77 or movement ofmagnetic armature 78, causing latch plate 67 to release primary latch65,

which in turn releases secondary latch 53 and permits main operatingsprings 38 to rotate cradle 40 in a counterclockwise direction to breaktoggle 42, 43. The force from main spring 38 acts through cradle 40,primary latch 53, and secondary latch 65 to drive cam surface 78,bounding opening 72, against extension 71 to rotate carrier 66clockwise, with surface 79 thereof engaging ear 81 of extension 82 ontripper bar 80 which extends between all three phases. This causestripper bar 80 to rotate in a counterclockwise direction, so thatextensions 82 in the non-faulted phases rotate" counterclockwise withcam surfaces 83 thereof engaging transversely extending pin 84 ofcarriers 66 in the nonfaulted phases, rotating them clockwise or in thetripping direction, to release the cradle latching systems in thenon-faulted phases, so that the contacts of all three phases are open.

In order to prevent closing of the contacts of any one phase before theoperating mechanisms of all phases are latched, circuit breaker 25 isprovided with a defeater latching system including defeater latch 80 anddefeater lever 90. Latch 80' is pivotally mounted upon rod 55 andincludes protrusion 81' extending over the rear of cradle 40 when thelatter is in latched position.

Latch further includes protrusion 82 extending over the forward end ofdefeater lever in slot 91 thereof. Coiled tension spring 83 is connectedbetween stop rod 57 and latch 80, passing partially around rod 55, tobias latch 80 in a counterclockwise direction about its pivot 55 andmaintaining this pivot in the basic position at the right end of slot 84in latch 80. This basic position is established through the engagementof latch stop surface 86 and stop rod 57.

Slot 91 is in the web of the U-shaped forward portion of latch lever 90,with the U arms having pivot pin 69 for lever 90 extending therethrough.Rear portion 89 of lever 90 is positioned below and in interferingrelationship with transverse pin 71 mounted to latch plate carrier 66.

During normal relatching of circuit breaker 25, inwardly protrudingportions of the operating member 35 arms engage outboard portions of pin44 to pivot cradle 40 clockwise, whereby the latter cams defeater latch80' away and moves below auxiliary latch 53. Upon release of the circuitbreaker operating handle 30, the elements of the latch train 53, 65, 66move into place. However, should any of these elements fail to properlyengage or should cradle 40 not have been moved far enough'to engageauxiliary latch 53, cradle 40 will pick up defeater latch protrusion 81causing clockwise rotation of defeater latch 80'. In turn, this causesdefeater latch protrusion 82' to engage defeater lever 90 and rotate thelatter counterclockwise with the rear end 89 thereof contacting carrierextension 71 so that latch plate carrier 66 is pivoted in a clockwise orlatch train releasing direction. During this releasing movement ofcarrier 66, surface 79 thereof engages nose 81 of one trip bar extension82 to rotate common tripper bar 80 in a counterclockwise direction, withthe other extensions 82 on bar 80 engaging pins 84 on the latch platecarriers 66 of the other poles, thereby causing the latch systems of allother poles to be released.

The lower end of bimetal 77 is fixedly secured to shading coil 99, andthese elements are fixedly secured to molded frame member secured totrip unit frame 60. The horizontal leg of inverted U-shaped stationarymagnetic frame member 98 passes through the center of coil 99. Member 98is secured to the rear of frame 60, with the vertical legs of member 98being on opposite sides of load strap 61. The other U-shaped magneticframe member 96 is secured directly to load strap 61, with the ends ofthe arms for frame members 96 and 98 confronting one another in spacedrelationship. Thus, current flowing in load strap 61 generates flux inmagnetic frame 96, 98 which induces current flow in shading coil 99 andthereby generates heat that is conducted to bimetal 77 for heatingthereof. Coiled tension spring 97, connected between armature 78 and anelement mounted to the rear transverse part 60 of frame 60, biases theformer away from two spaced legs 98a extending upward from thehorizontal leg of member 98, and is drawn downward toward legs 98a whenoverload currents generate sufficient magnetic flux in magnetic frame78, 96, 98.

With particular reference to FIG. 4, it is seen that the movable contactstructure for each phase of circuit breaker 25 includes eight maincontacts 103-110 and a single arcing contact 101. The latter contact 101is mounted at the forward end of arm 112, which is pivotally mounted tocarrier 45 at toggle connecting rod 46. Main contacts 103-110 arearranged in two parallel rows positioned to the rear of arcing contact101 and disposed at right angles to the plane of movement of arcingcontact arm 112.

Main contacts 103-106 in the forward row are mounted to individualcontact arms 113-116 respectively, all pivotally mounted to carrier 45on rod 46. Main contacts 107-110 in the rear row are mounted to theforward end of the respective contact arms 117-120, respectively,pivotally mounted to carrier 45 on rod 102. All of the contact arms112-120 are connected to load strap 61 by means of individual stacks 121of flexible sheet conductors. Contact arms 113-116 are in alignment withand extend over the respective contact arms 117-120, so that the lattergroup of arms 117-120 block downward movement of the former group ofarms 113-116 to establish the open circuit position of contacts 103-106in a manner which will hereinafter be seen. The open circuit positionfor arcing contact arm 112 is established through engagement thereofwith aligned pins 123, 124 which mount the respective pairs of maincontacts 117, 118 and 119, 120 to auxiliary carriers 125, 126respectively. Notch 122 along the lower edge of arcing contact arm 112provides clearance for pins 123, 124.

Auxiliary carrier 125 is an inverted U-shaped member whose arms extenddownwardly through cutouts 131, 132 in the web portion of contactcarrier 45 and straddle four contact arms 113, 114, 117, 118. Pin 123secures contacts 117, 118 to the lower ends of the arms comprisingauxiliary carrier 125. The web of auxiliary carrier 125 is biasedtowards the web of contact carrier 45 by coiled compression spring 127,which is wound around the threaded body of bolt 128 whose head ispositioned below the web portions of contact carrier 45. Self-lockingnut 133 mounted to bolt 128 is rotated to adjust the loading of spring127, with the rectangular shoulder of bolt 128 cooperating withrectangular cutout in carrier 45 to prevent rotation of bolt 128. Thus,in the open circuit position, spring 127 biases the web of auxiliarycontact carrier 125 against the web of contact carrier 45, and when thecontacts are closed there is a space between the webs of these contactcarriers 45, 125, so that the force exerted by spring 127 acts to biascontacts 107, 108 into firm electrical engagement with their respectivecooperating contact portions on line strap 136.

The mounting of contact arms 119, 120 to auxiliary contact carrier 126and mounting of the latter to contact carrier 45 is the same as themounting of contact arms 117, 118 and auxiliary carrier 125, so thatthis description will not be repeated.

Biasing forces for each of the contacts 103-106 in the forward row areprovided by individual coiled compression springs 138, and each of thesesprings is mounted in the same way so that only the mounting of one ofthese springs will be described. The lower end of spring 138 extendsinto depression 139 in the upper surface of main contact arm 113, andthe rear of spring 138 extends into tubular support 141 through the openbottom thereof. Support 141 is mounted to the upper surface of carrier45 at the web portion thereof, and its upper end is threaded to receiveadjusting screw 142 whose lower end bears against disc 143 abutting theupper end of spring 138. If screw 142 is adjusted to set the contactpressure exerted by spring 138, lock nut 144 is tightened to lock thisadjustment.

In order to increase the area of engagement between main contacts103-110 and their respective cooperating stationary main contacts in thevery limited space available, it is noted that each of the main contactsis provided with a portion extending outward of its respective contactarm. That is, in order to utilize the space below arcing contact 112,main contacts 104, 105, 108, 109 have been extended beyond theirrespective contact arms 114, 115, 118, 119 to project below 1 arcingcontact arm 112. Similarly, main contacts 103, 106, 107, have beenextended outboard from their respective contact arms 113, 1 16, 117,120, to lie in the space below the outboard arms of auxiliary contactcarrier 125, 126 and other elements used to connect the movable contactstructure to the contact operating mechanism.

The forward end of arcing contact arm 112 is biased downward away fromthe web portion of contact carrier 45 by coiled compression spring 171whose lower end is positioned by pin 172 extending upward from arm 112.The upper end of spring 171 extends into tubular member 173, on theupper surface of the carrier 45 web portion, through the bottom ofmember 173 and abuts the closed upper end thereof.

The spaced arms of contact carrier 45 are provided with rearwardextensions 45a, 45b that are spaced by and secured to shoulderedcylindrical tube 146. After all contact structures, operatingmechanisms, latching devices, and automatic trip units are mounted tobase 26, and all adjustments to these mechanisms have been made, thecontact structures of all phases are operated to the closed circuitposition, so that the tubular members 146 of all phases are axiallyaligned and are positioned above barriers 31, 32 and the longitudinalsides of base 26. Thereafter, cylindrical tie bar 147 is drivenlongitudinally in the members 146 of all phases to constitute a rigidmechanical connection between the movable contact structures of allphases. The fit between tie rod 147 and tubular members 146 is tightenough to prevent unintentional axial movement of tie rod 147, yetpermits tie rod 147 to be removed for convenient servicing andreplacement of parts. Mechanism frame 36 is provided with alignedelongated slots 148 to provide clearances for movement of rod 147 duringopening and closing of the movable contact structures.

Auxiliary handle operating mechanism (FIGS. 2, 5 and 6) is mounteddirectly to the front of cover 27 by four screws 251 located at oppositecorners of shallow rectangular molded housing 252. Molded main operatinghandle 253 is positioned outside of housing 252 and is keyed to stubshaft 254 so as to be pivotable in a plane parallel to the front ofhousing 252. Shaft 254 is journaled by circular apertures in closelyspaced parallel support plates 257 and 258. Plates 257 and 258 aresecured together as part of an assembly which, for the most part, isdisposed within housing 252 and is secured thereto by four bolts 259.

Parallel closely spaced plate-like sections 256a, 2561; forming dricelink 256 are joined at their left ends (with respect to FIGS. 5 and6)-at connecting part 256a, and at this region drive link 256 is keyedto shaft 254. Main link 260 is freely mounted at its right end (withrespect to FIGS. 5 and 6) on stub shaft 261 whose ends are held incircular apertures of support plates 257, 258. Links 256, 260 extendtoward one another and are provided at their respective free ends withlongitudinally extending slots 263, 264 which receive roller portions ofcon- 7 necting means 265. Other roller portions of connecting means 265act as followers, being disposed in aligned cam slots 266 in supportplates 257, 258.

The central portion of main link 260 is provided with i cutout 267wherein spaced rollers 268, 269 are disposed. Stub shafts 271, 272,whereon the respective rollers 268, 269 are freely mounted, are disposedwithin circular apertures of retainer plates 273 secured on oppositesurfaces of main link 260 by four rivets 274. Roller 222, mounted onextension 33 of circuit breaker handle 30, is disposed between rollers268, 269 so as to be engageable thereby for transfer of motion from mainoperating handle 253 to circuit breaker handle 30.

Thus, it is seen that a force supplied to pivot arm 253 is applieddirectly to drive link 256 which acts through connecting means 265 topivot main link 260. This motion of link 260 causes the arcuate surfaceof one or the other of rollers 268, 269 to engage the arcuate surface ofroller 222 on circuit breaker handle extension 33 to thereby pivotcircuit breaker handle 30 for opening and closing of circuit breaker 25depending upon the direction of movement of main operating handle 253.

It is noted that cam slots 266 force pin-roller connecting means 265 totravel along a predetermined path, and in this manner the effectiverelative lengths of links 256, 260 are varied in accordance with theposition of handle 253. The effective lengths of links 256, 260 are thedistances between the connecting means 265 and the respective fixedpivots 254, 261. In the embodiment illustrated, cam slot 266 is an aredrawn about a center located to the left of fixed pivot 254 as seen inFIGS. and 6. The shape of cam slot 266 and its location with respect tofixed pivots 254, 261 are chosen so that the mechanical advantageafforded by main operating handle 256 and link system 256, 260 varies inaccordance with the force required to operate the contact operatingmechanism.

The force that must be applied to handle 253 is also minimized by havingthe driving connection between auxiliary mechanism 250 and circuitbreaker operating handle 30 take place between roller 222 and rollers268, 269, all of which are freely rotatable. This essentially eliminatesfrictional engagement. This arrangement also permits rollers 222, 268,269 to be of substantially uniform diameters throughout the lengthsthereof.

It is noted that because of high magnitude current flow in circuitbreaker 25, the magnetic fields generated are very strong. In order toreduce adverse effects of these magnetic fields, many of the frame partsand operating mechanism parts are constructed of nonmagnetic stainlesssteel.

For those features of construction in circuit breaker 25 that have notbeen described in detail herein, reference is made to one or more of thecopending applications Ser. Nos. 275,568, 275,577, 275,446, 275,578,

275,454, 275,508, 275,621, 275,623, 275,624, 275,569, 275,522, 275,521,275,523, and 275,622, all filed of even date herewith, and all assignedto the assignee of the instant invention.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now become apparent tothose skilled in the art. Therefore, this invention is to be lim itednot by the specific disclosure herein but only by the appending claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

l. The combination comprising a circuit breaker and an auxiliary handlemechanism mounted thereto; said circuit breaker including an enclosurehaving a front wall, and a spring powered overcenter toggle contactoperating mechanism including a contact operating handle having anextension projecting through an opening in said front wall and mountedfor pivotal movement in a first plane; said auxiliary handle mechanismincluding support means, a main operating handle mounted in front ofsaid support means, a lever pivotally mounted to said support means andoperatively connected to said main operating handle means to be operatedthereby in a second plane at right angles to said first plane; saidlever having spaced formations between which said extension of saidcontact operating handle is disposed; a first roller mounted on saidextension to rotate freely on an axis perpendicular to said first plane;said spaced formations including second and third rollers laterallyspaced and disposed with the axis of said first roller passingtherebetween; said second and third rollers being engageable with saidfirst roller to transmit motion of said lever to said contact operatinghandle; said second and third rollers being mounted on said lever torotate freely on axes generally perpendicular to said second plane.

2. A combination as set forth in claim 1 in which the extension of thecontact operating handle is constructed of insulating material; saidfirst, second and third rollers being constructed of material generallyhaving the wear-resistant properties of a hardened steel.

3. A combination as set forth in claim 1 in which the engaging surfacesof said first, second and third rollers are cylindrical.

4. A combination as set forth in claim 3 in which said engaging surfacesare substantially of uniform diameter throughout their respectivelengths.

5. A combination as set forth in claim 4 in which the extension of thecontact operating handle is constructed of insulating material; saidfirst, second and third rollers being constructed of material generallyhaving the wear-resistant properties of a hardened steel.

1. The combination comprising a circuit breaker and an auxiliary handlemechanism mounted thereto; said circuit breaker including an enclosurehaving a front wall, and a spring powered overcenter toggle contactoperating mechanism including a contact operating handle having anextension projecting through an opening in said front wall and mountedfor pivotal movement in a first plane; said auxiliary handle mechanismincluding support means, a main operating handle mounted in front ofsaid support means, a lever pivotally mounted to said support means andoperatively connected to said main operating handle means to be operatedthereby in a second plane at right angles to said first plane; saidlever having spaced formations between which said extension of saidcontact operating handle is disposed; a first roller mounted on saidextension to rotate freely on an axis perpendicular to said first plane;said spaced formations including second and third rollers laterallyspaced and disposed with the axis of said first roller passingtherebetween; said second and third rollers being engageable with saidfirst roller to transmit motion of said lever to said contact operatinghandle; said second and third rollers being mounted on said lever torotate freely on axes generally perpendicular to said second plane.
 2. Acombination as set forth in claim 1 in which the extension of thecontact operating handle is constructed of insulating material; saidfirst, second and third rollers being constructed of material generallyhaving the wear-resistant properties of a hardened steel.
 3. Acombination as set forth in claim 1 in which the engaging surfaces ofsaid first, second and third rollers are cylindrical.
 4. A combinationas set forth in claim 3 in which said engaging surfaces aresubstantially of uniform diameter throughout their respective lengths.5. A combination as set forth in claim 4 in which the extension of thecontact operating handle is constructed of insulating material; saidfirst, second and third rollers being constructed of material generallyhaving the wear-resistant properties of a hardened steel.